The major objective of this project will be to determine whether genetic variation in the structure or quantity of the enzymes involved in flight metabolism cause variation in the power output of the flight muscles of Drosophila melanogaster. The power output will be estimated from the wing morphology and the frequency and amplitude of the wing-beat of tethered flies. Homozygous lines, in which chromosomes sampled from natural populations are substituted into an isogenic background, will be screened for associations among allozyme type for three enzymes, activity for a number of enzymes and the flight parameters that determine power output. Some experiments are also proposed to investigate the specificity of the association between wing-beat frequency and mitochondrial enzyme activities that we have already observed. Because the metabolic rate of flight muscles of insects is much greater than for any other type of muscle, this system should provide a sensitive measure of the physiological effects of enzyme variants.